Phil Unitt, curator of Birds and Mammals for the San Diego Natural History Museum, and Jennifer Lee a biologist from UC Riverside, worked to free a Wilson's Warbler from one of the mist nets set up in Tahquitz valley.
— John Gibbins / John Gibbins/UT San Diego

Volunteer packers carried the equipment up the steep Devil's Slide trail for the San Diego Natural History Museum biologists that are resurveying a section of the San Jacinto mountains near Idyllwild that was originally done in 1908 to compare data.
— John Gibbins / John Gibbins/UT San Diego

Packers who brought the expeditions' heavy gear up to their base camp readied to return down the mountain. They would return in a week at the end of the expedition to take everything back down.
— John Gibbins / John Gibbins/UT San Diego

San Diego Natural History museum biologists Brad Hollingsworth, left, and Scott Timor, right, readied their hand held gps units before heading out on the first day of the expedition. Everything related to the project is precicesly located with the devices.
— John Gibbins / John Gibbins/UT San Diego

Phil Unitt, curator of Birds and Mammals for the San Diego Natural History Museum, and Jennifer Lee a biologist from UC Riverside, worked to free a bird from one of the mist nets set up in Tahquitz valley.
— John Gibbins / John Gibbins/UT San Diego

Phil Unitt, curator of Birds and Mammals for the San Diego Natural History Museum, prepared a bird specimen by the light of a gas lantern and headlight at the base camp.
— John Gibbins / John Gibbins/UT San Diego

Phil Unitt, curator of Birds and Mammals for the San Diego Natural History Museum,set up a mist net, used to collect bird specimens, along a creek in the Tahquitz Valley.
— John Gibbins / John Gibbins/UT San Diego

Phill Unitt, front, called for a golden Crowned Kinglet that he briefly spotted in the tops of the trees while Jennifer Gee, middle and Thomas Myers, rear, scanned for it.
— John Gibbins / John Gibbins/UT San Diego

Field biologists from the San Diego Natural History Museum are resurveying a section of the San Jacinto mountains near Idyllwild that was originally done in 1908 to compare data.
— John Gibbins / John Gibbins/UT San Diego

As of the middle of the second day of the exhibition, the biologists had prepared four bird and two mammal specimens that would be brought back to the Museum's permanent collection.
— John Gibbins / John Gibbins/UT San Diego

Tony Harper, a part time field biologist for the Museum who volunteered for this project, used an auger to dig a hole for traps used to catch insects, rodents or reptiles that might pass by.
— John Gibbins / John Gibbins/UT San Diego

Brad Hollingsworth, curator of herpetology at the museum was looking for the federally endangered yellow-legged frog in a creek at Laws Crossing in the Tahquitz Valley. After hiking several miles of the stream, he was unsuccessful.
— John Gibbins / John Gibbins/UT San Diego

Brad Hollingsworth, curator of herpetology at the museum was looking for the federally endangered yellow-legged frog in a creek at Laws Crossing in the Tahquitz Valley. After hiking several miles of the stream, he was unsuccessful.
— John Gibbins / John Gibbins/UT San Diego

Tony Harper, a part time field biologist for the Museum who volunteered for this project prepared a vole, a small mammal, that was caught in a trap, for the museum collection.
— John Gibbins / John Gibbins/UT San Diego

IDYLLWILD, Calif.  As the orange light of sunrise broke across the San Jacinto Mountains one recent morning, biologists from the San Diego Natural History Museum fanned out across the high country to retrace the steps of a pioneering scientist who first cataloged the region’s wildlife more than a century ago.

On and off for the past five years, the museum’s team has methodically deployed traps, nets, motion-sensing cameras and other devices to survey animals at numerous sites in the San Jacinto range. Their inspiration is zoologist Joseph Grinnell, who spent about four months in the area in 1908 and left behind nearly 600 journal pages.

Grinnell noted his hope that future scientists would tap his data. The crew from San Diego is using those details to assess the effects of urbanization on animal life and the potential for global warming to force creatures higher up the slopes as they seek refuge from the heat — questions that could take years to answer conclusively.

As the museum’s “centennial resurvey” circles toward completion next year, preliminary conclusions are as complex as the landscape; some areas of the San Jacinto range appear to be in more natural condition today because there are fewer cattle grazing, while other sites have been transformed by houses and repeated fire.

Faunal records have yielded intriguing results: field biologist Drew Stokes found a mountain yellow-legged frog near Tahquitz Valley three years ago, expanding the area where the nearly extinct frogs are known to live. In addition, museum experts are investigating the dramatic reduction — or even the local demise — of species such as gray vireos, flying squirrels and lodgepole chipmunks that Grinnell found the San Jacinto range.

“The data will tell us stories — things we haven’t seen yet — (when) it’s all pulled together,” said Scott Tremor, a mammalogist at the museum.

Some mysteries may linger for another century, and members of the expedition expect their work will enable future generations of scientists as they try to make sense of the natural world.

“Evolution is unpredictable. You could think you see something in five years and then there will be an El Niño and things will shift dramatically,” said Jennifer Gee, director of the University of California’s James San Jac­into Moun­tains Reserve, who has helped the San Diego team. “You have got a really complicated system. That we (humans) have disturbed it makes it that much more complicated. We are getting as much signal from that noise as we can.”

Southern California was mostly wild when Grinnell started taking stock of the San Jacinto Mountains. He took copious notes in tiny script, filling journals with entries about every creature that crossed his path — many of which he shot dead so he could study them.

His writings were less lyrical than those of conservationist John Muir, a Grinnell contemporary famous for his love of the Sierra and stylish prose about his mountain wanderings.

While Muir founded the Sierra Club and the modern environmental movement, Grinnell launched the Museum of Vertebrate Zoology at UC Berkeley, which today houses more 640,000 specimens, making it one of the largest collections in the nation. Grinnell also developed protocols for standardizing observations, a cornerstone of systematic biology.